In the production of color photographic images, it is necessary to remove the silver image which is formed coincident with the dye image. This can be done by oxidizing the silver by means of a suitable oxidizing agent, commonly referred to as a bleaching agent, in the presence of halide ion, followed by dissolving the silver halide so formed in a silver halide solvent, commonly referred to as a fixing agent. Alternatively, the bleaching agent and fixing agent can be combined in a bleach-fixing solution and the silver removed in one step by use of such solution.
A wide variety of bleaching agents are known for use in photographic processing, for example, ferricyanide bleaching agents, persulfate bleaching agents, dichromate bleaching agents, permanganate bleaching agents, ferric chloride, and water-soluble quinones.
It is particularly well known to use a ferric complex of an aminopolycarboxylic acid as a bleaching agent in photographic color processing. Such complexes are used in both bleaching compositions and bleach-fixing compositions. A very large number of different compounds of the aminopolycarboxylic acid class are disclosed in the prior art as being useful photographic bleaching agents. However, the usual commercial practice is to use an ammonium or alkali metal salt of a ferric complex of ethylenediaminetetraacetic acid (EDTA) or of a ferric complex of propylenediaminetetraacetic acid (PDTA).
Among the numerous patents describing the use of ferric complexes of aminopolycarboxylic acids in bleaching and/or bleach-fixing baths are U.S. Pat. Nos. 3,241,966, 3,615,508 and 3,767,401 and British patent Nos. 1,365,453, 1,392,163, and 1,394,357.
It is well known in the photographic art to utilize a stabilizing bath as the final step in the processing of both color films and color papers. Such baths can serve to reduce stain and/or enhance dye stability. A wide variety of different stabilizing compositions have been proposed for such use. Thus, the known stabilizing baths include those containing thiourea or a substituted thiourea as described in Kellog, U.S. Pat. No. 2,487,446 issued Nov. 8, 1949; aliphatic aldehydes as described in Harsh et al, U.S. Pat. No. 2,518,686 issued Aug. 15, 1950; addition products of formaldehyde and a urea, as described in Mackey, U.S. Pat. No. 2,579,435 issued Dec. 18, 1951; tetramethylol cyclic alcohols or ketones as described in Clarke et al, U.S. Pat. No. 2,983,607 issued May 9, 1961; glucoheptonates as described in Bard, U.S. Pat. No. 3,157,504 issued Nov. 17, 1964; carbohydrazides as described in Larson, U.S. Pat. No. 3,201,244, issued Aug. 17, 1965; amino acids as described in Jeffreys, U.S. Pat. No. 3,291,606 issued Dec. 13, 1966; mixtures of an aldehyde and an alkoxy-substituted polyoxyethylene compound as described in Seemann et al, U.S. Pat. No. 3,369,896 issued Feb. 20, 1968; compounds comprising a tri(hydroxymethyl)methyl group as described in Jeffreys et al, U.S. Pat. No. 3,473,929 issued Oct. 21, 1969; and addition complexes of an alkali metal bisulfite and an aldehyde as described in Mowrey, U.S. Pat. No. 3,676,136 issued July 11, 1972. The use of more than one active agent in such stabilizing baths is also known. For example, U.S. Pat. No. 3,676,136 to Mowrey describes the use of antioxidants such as glucose, galactose, sorbitol or mannitol in a stabilizing bath in addition to an aldehyde bisulfite addition complex.
Magenta dye stability is a particularly serious problem in color photography, as the magenta dye image tends to fade much more rapidly than either the cyan dye image or the yellow dye image. The dark-keeping stability of magenta image dyes derived from pyrazolone couplers is adversely affected by the presence of the coupler itself. This is particularly evident in the toe and midscale regions of the green sensitometric curve. In these areas, there is a substantial amount of the unreacted coupler. This unreacted coupler undergoes complex chemical reactions with the magenta dye.
For many years, formaldehyde has been commonly used as a stabilizing agent in photographic color processing to provide enhanced magenta dye stability. The photographic element is treated with a final bath--called a "stabilizing bath"--that contains formaldehyde. The formaldehyde reacts with the unused coupler in the film, forming a stable compound that will not react with the magenta dye. Under normal processing conditions, this reaction is completed in the drying oven. However, while formaldehyde is a very effective stabilizing agent for this purpose, its use is highly disadvantageous from an ecological standpoint because of the well known ecological concerns relating to formaldehyde.
It is toward the objective of providing an improved bleaching composition that provides effective bleaching action and also provides improved dye stability, so as to eliminate the need for a stabilizing bath, that the present invention is directed.